1. Field of the Invention
This invention generally relates to a rotary portion, which has a flexible plate to be flexible in a bending direction. More specifically, the present invention relates to flywheel assemblies and torque converters in which a dynamic damper is coupled thereto to absorb vibrations.
2. Background Information
A flywheel is usually installed in an engine of a car to prevent rotary fluctuations at the low speed range of the engine. In the flywheel, a clutch device and a ring gear are usually installed. The engine generates a driving power by converting the combustion force generated by combustion of the fuel into a torque that rotates a crankshaft. At that time, a bending force is exerted on the crankshaft when, the engine converts the combustion force into a torque that rotates a crankshaft. The crankshaft is then bent by the combustion, resulting in a bending vibration on the flywheel in a bending direction. The reaction force from the vibration of the flywheel is transmitted to the engine block, which further vibrates the body of the car via the engine mount. This results in a considerable amount of noise during acceleration of the engine.
In order to reduce noise during acceleration of the speed of the engine, the flywheel is connected to the crankshaft by a flexible plate. The flexible plate is usually a thin disk-shaped member or a thin cross-shaped member, which has a high rigidity in the direction of rotation and a low rigidity in the direction of the bending vibrations. When bending vibrations are transmitted, the flexible plate absorbs the vibrations by bending in the bending direction (generally axially), resulting in a reduction of vibrations on the flywheel.
As shown in FIG. 5, a vibrational characteristic of a conventional flywheel is illustrated. The dotted line of FIG. 5 represents a characteristic of a flywheel assembly in which the flywheel is fixed directly to the crankshaft without a flexible plate. The solid line of FIG. 5 represents a characteristic of a flywheel assembly which has a flexible plate coupled between the flywheel and the crankshaft.
In the characteristic of the dotted line (without a flexible plate) shown in FIG. 5, the resonance frequency exists within a normal range A. In the characteristic of the solid line (with a flexible plate) shown in FIG. 5, the resonance frequency is divided into two sections. Both sections of resonance frequencies have a vibration level (bending angle of a flywheel) which is lower than the resonance frequency of the characteristic of the dotted line (without flexible plate). In addition, the two sections of resonance frequencies are shifted into high and low frequency sides from a normal range A, respectively. Thus, by shifting the resonance frequencies from the normal range A, noise can be reduced during acceleration of the speed of the engine.
However, in the characteristic of the solid line (with flexible plate) of FIG. 5, the resonance frequency on the low frequency side sometimes remains in a normal range A. In that case, nevertheless, the noise is caused during acceleration of the speed of the engine. An object of the present invention is to reduce a noise in accelerating the speed.
In view of the above, there exists a need for flywheel assemblies and torque converters with dynamic dampers which overcome the problems in the prior art devices. This invention addresses these needs in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.